The invention relates to a hydraulic control system for controlling a plurality of consumers and to a pressure governor for such a hydraulic control system.
Hydraulic control systems according to the present invention are used particularly in mobile machines such as wheel loaders or tractors in order to supply pressure fluid to their consumers, e.g. the working hydraulics, the steering, traveling mechanisms, and/or accessories. DE 41 27 342 C2 has disclosed hydraulic control systems that are embodied in the form of LS systems. In LS systems of this kind, the delivery quantity of the pump is regulated so that in the pump line, a pump pressure prevails that lies a certain pressure difference Δp above the maximum load pressure of the consumers. In the known systems, each consumer is associated with an adjustable metering orifice and an individual pressure governor by means of which the volumetric flow of pressure fluid to the consumer can, independent of the load, be kept constant as a function of the setting of the metering orifice. In these LS systems, downstream of the pump, an inlet pressure governor can be provided, which can open a connection to the tank. These inlet pressure governors are acted on in the closing direction by a control pressure that corresponds to the maximum load pressure. The pressure difference at which the inlet pressure governor opens is as a rule set slightly higher than the pressure difference Δp set by means of the pump.
In order to connect attached devices or accessories that do not have their own supply of pressure fluid, a so-called power beyond connection is provided, which can have a pressure line, a return line, and an LS line. This power beyond connection permits the load-sensing system of the machine to also be used for the attached device.
DE 10 2004 048 684 is an example of a hydraulic control system provided with a power beyond connection. In this control system, the pump connection of a power beyond pressure governor is provided in a flow path between the pressure connection of the pump and the pump connections of the pressure governors of the other consumers. The power beyond pressure governor is connected in series with the power beyond consumer. A disadvantage of this known embodiment is the fact that the activation of the power beyond consumer can lead to uncontrolled behavior of one or more consumers, particularly in the event of an undersupply. Since the volumetric flow demand of the power beyond consumer is not as a rule known, the valve control and pump control cannot be adapted to the requirements of the power beyond consumer.
In relation to this prior art, the object of the invention is to create a hydraulic control system suitable for this purpose as well as a control method, which both assure a demand-actuated pressure fluid supply to all consumers when at least one power beyond consumer is connected to a power beyond connection.
According to the invention, a hydraulic control system is provided for controlling at least two consumers that can be supplied with pressure fluid by a pump with an adjustable delivery quantity and that are each associated with an adjustable metering orifice. This hydraulic control system is preferably used in mobile machines and has a power beyond connection for the connection of a power beyond consumer and one inlet pressure governor, which is connected downstream of the pump. This inlet pressure governor can open a connection to the tank and can be adjusted as a function of a load pressure of the consumer or of the at least one power beyond consumer. The placement of the inlet pressure governor in the pressure fluid flow path between the pump and at least one of the consumers as well as the branching of the power beyond connection from a pressure fluid flow path between the pump and the inlet pressure governor assures a prioritized supply of the power beyond consumer.
The pump can preferably be controlled as a function of the setting of the inlet pressure governor, thus yielding a demand-actuated supply of the consumers. In particular, the pump is controlled as a function of the position of a control piston of the inlet pressure governor thus permitting a precise regulation to be carried out in an inexpensive fashion.
A control of the pump as a function of the volumetric flow in a connection of the inlet pressure governor permits direct sensing of hydraulic parameters in order to selectively influence the pump regulation with favorable dynamic properties.
A signal for triggering the metering orifice of at least one consumer can also be used as a parameter for the pump control. As a result, the position and/or residual flow regulation of the inlet pressure governor no longer has to compensate for any more than relatively slight regulating deviations.
Preferably, the maximum of the load pressures acts on the inlet pressure governor in the closing direction so that the load sensing system of the consumers can also be used for the power beyond consumer.
According to an advantageous modification of the invention, the inlet pressure governor closes the connection to at least one consumer and the tank in a spring-prestressed starting position; when moved in the opening direction, it opens the connection to at least one of the two consumers and when moved further in the opening direction, opens the connection to the tank. A sufficient supply to all consumers is then assured if the residual volumetric flow is discharged to the tank via the open inlet pressure governor.
The inlet pressure governor is preferably acted on in the closing direction by the force of at least one spring and by the maximum of the load pressures and is acted on in the opening direction by the pressure at the inlet of the inlet pressure governor.
In a preferred control system, the inlet pressure governor is provided with a spring packet or a progressive spring for acting on it in the closing direction and for switching the regulating pressure difference, thus making it possible to implement a travel-dependent change in the spring force on a control piston of the inlet pressure governor.
According to another preferred embodiment of the present invention, in order to increase the regulating pressure difference, the control system is provided with a device for increasing the prestressing force of the spring, which produces this increase mechanically, hydraulically, or electrically. This permits the control of the inlet pressure governor to be adapted to special structural circumstances and permits the control of the inlet pressure governor control piston to also be implemented over greater distances by the operator of a machine.
The pump is preferably an electrically controllable variable displacement pump or a speed-regulated fixed displacement pump, thus making it possible to implement the pump regulation in an inexpensive fashion.
It is particularly advantageous if each metering orifice has an individual pressure governor connected upstream of it, which can be acted on in the opening direction by the respectively associated load pressure of the associated consumer and by a pressure governor spring and can be acted on in the closing direction by the pressure at the outlet of the individual pressure governor. This yields a rapidly reacting load sensing system.
The metering orifices are preferably comprised of electrically, hydraulically, or mechanically movable directional control valves.
According to the invention, a pressure governor is also provided for one of the control systems described above; the control piston of this pressure governor can be acted on in the closing direction by a pressure governor spring arrangement and can be acted on in the opening direction by a load pressure. This pressure governor spring arrangement preferably has two springs that can be brought into engagement one after the other and that make it possible for the inlet pressure governor to take up a small amount of installation space.
In a control method according to the invention, the regulating pressure difference at the inlet pressure governor is increased with the activation of the power beyond consumer so that in addition to the prioritization of the power beyond consumer, an increase in the regulating pressure difference is also assured in order to permit a reliable operation of attached devices, even in the event of significant pressure drops in the line system leading to the attached device.
Advantageous modifications of the invention are the subject of the dependent claims.